The best method is to use seismic refraction technique. This gives a well definition of soil profile and sinkhole can be detected.

A sinkhole is a localized depression in the surface of the ground that was caused by the removal of underlying material. Soil test borings are usually drilled to auger refusal to check the variability of the bedrock surface. It is common to find soft soil conditions and an erratic rock surface in active sinkhole areas. There are several viable options to consider for sinkhole risk reduction. 1. Rock Supported Foundations 2. Grouting techniques 3. Surface Stabilization Layer 4. Excavation and Placement of Inverted Rock Filter

In my experience, the Borehole Drilling Process is a very important and crucial activity must be done perfectly at early stage in the project. I do believe that about 80% of the true knowledge and assessment of the soil properties, is resulted in from the works done in the site itself. The remaining 20% will be taken from laboratory tests. Furthermore, in big and national projects, another investigation study must be done before the geotechnical investigation, which is the Geophysical Survey. There are two important benefits will be gained; 1) the verification of the specific site properties in hand either from back history of the soil consultant, or soil handbook data , 2) the results of the geophys. invest. will lead to opt. BH location.

The Standard Penetration Test (SPT), in particular, is a vital tool for determining the causes of sinkholes in geotechnical field testing. A split-barrel sampler is driven into the ground as part of the SPT, and the number of blows needed to penetrate the soil is recorded. Sinkholes are frequently caused by collapsing subterranean voids or overlying karst formations. Engineers can evaluate soil density variations, spot possible voids, and calculate the likelihood of sinkhole formation by analysing SPT data, which can help with mitigation measures.

In my experience, the Standard Penetration Test and the following mentioned tests surly can detect changes in soil characteristics due to environmental conditions in a specific location of the site under study; like weathering, erosion, etc., which can increase the susceptibility of formation of sinkhole or cavities which may lead in turn to sudden failure. Some tests are more identifying the soil than others, like for example, the SPT is leading for cohesionless soil like sandy soil, and CPT leading cohesion soil like clayey soil.

Determine the cause of a sinkhole and developing a repair plan typically involves geotechnical engineers, geologists, & other experts. Step involved; 1. Site investigation: engineers start by conducting a through site investigation. This includes surveying the sinkhole area, examining the geological conditions, & collecting relevant data such as soil samples, groundwater level, &other geotechnical information. 2. Geological analysis: the collected data is analyzed to understand the soil composition, the presence of water, & other factors that may have to contribute to the formation of the sinkhole. 3. Geological analysis 4. Remote sensing techniques 5. Cause determination 6. Repair plan development 7. Risk mitigation

As a very good example to agree on the importance of the site testing mentioned above in a quite comprehensive summary, and to what extent, these tests must be done properly and supervised efficiently by the client consultant, this example is a national project I’ve participated in, it was crude storage tank 60 meters diameter. Reviewing the load test results, I noticed a contradiction between such results and those estim. settlement values in the soil inv. report. Some values reversed and some measured settl. values are bigger (almost double) the estimated ones which opposite the norms which say that, the measured settl. values are around 50% of the predicted in report.The reason was Cavities missed in report and detected in new BH’s done.